"Miniature Aero Motors" is an early 1949 publication from Ian Allan Ltd. of London, England. This little 160 page hardcover volume was authored by Ron Warring (d. 1984), who was one of the most prolific and wide-ranging aeromodelling authors of his or any other day. Although his primary focus in the model contest field was the rubber-powered Wakefield event, Warring was always fascinated by miniature I/C engines, going back to his 1930's association with "Jack" Colyer of Majesco Motors fame. This interest led him in later years to become the resident model engine tester for "Aeromodeller" magazine, replacing Lawrence Sparey in that role in June 1952.
Warring's 1949 book was the first British work to deal with the subject of model aero engines holistically rather than by specific type. It is primarily technical in nature, covering all aspects of model engine design, operation, maintenance and development potential in a series of 13 well-organized chapters. All types of model engines are included, from diesel, spark ignition and glow-plug down to jet units. There is relatively little in the way of historical information, but the book more than makes up for this by its technical content. Full construction details are provided of most of the model engine designs, both British and American, whch were available as of the latter part of 1948, when internal evidence suggests that the data was largely compiled. The book appears regularly as a data reference in my own historical articles.
Having said this, I must record the fact that my own research has uncovered a significant number of errors in the dimensions set out in Warring's tables. It appears that he was relying on others to provide much of this data, and some accuracy was evidently lost in the transfer. Moreover, it appears that the calculation of displacements from the cited figures was sometimes in error - the figures presented in the tables do not appear to have been checked in all cases. Finally, the cited weights often differ significantly from those obtained from present-day measurements taken from the engines.
If your primary interest is in the narrative history of model engine development, you won't learn much from this book. However, as an insighful look at then-prevailing theories regarding design, operation and further development of model engines, as well as a source of basic construction data on then-current models, this book has few rivals. The errors in the technical tables do not alter the fact that the book remains an invaluable reference.
